This invention relates to a process for regenerating an organouranium catalyst.
It is known that organouranium complexes are homogeneous catalysts for the selective dimerization of propylene to 4-methyl-1-pentene. Specifically, U.S. Pat. No. 4,695,669 discloses homogeneous catalysts comprising uranium di(poly-substituted cyclopentadienyl) hydride complexes for such a dimerization. Typically, the selectivity of these catalysts to 4-methyl-1-pentene is at least 94 percent with respect to all C.sub.6 products, as well as with respect to other C.sub.6 olefins; and often the selectivity is much higher. These uranium catalysts do not exhibit long lifetimes: hence, commercial application of the catalysts is costly and impractical.
In general, the industrial use of homogeneous catalysts is hampered by difficulties in recovering and recycling these catalysts. A homogenous catalyst is a soluble complex comprising inorganic and/or organic ligands and one or more metals. Generally, the deactivation of the homogeneous catalyst occurs because the complexhas decomposed and can no longer participate in the catalytic cycle. For example, the ligands, which form a crucial part of the homogeneous catalyst, might slowly react and dissociate from the metallic center. With loss of ligands the metal might precipitate from the reaction solution. It is also possible for several metal centers to react to form a catalytically inactive cluster. Alternatively, a by-product might bind irreversibly to the metal site and terminate the catalytic cycle. The regeneration process must replace the ligands and the metal(s) in a precise structure identical to that of the original active catalyst or catalyst precursor. The reorganization of a decomposed organometallic complex is rarely accomplished in simply one step. Typically, the metal is recovered and the complex is resynthesized. Such is the case, for example, in the regeneration of a spent homogeneous catalyst containing nickel and benzcate ligand, which is used in the oligomerization of ethylene to linear alpha-olefins. (See U.S. Pat. No. 3,676,523).
It would be desirable to have an economical, one-step process of regenerating the catalysts comprising di(poly-substituted cyclopentadienyl)uranium hydride complexes, cited hereinbefore. Such a regeneration process would render these uranium catalysts viable for commercial use in dimerizing propylene to 4-methyl-1-pentene.